The disclosure of Japanese Patent Application No. 2000-289643 filed on Sep. 22, 2000, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a friction engagement element combined with a lubrication system therefor and, more particularly, to a lubricating apparatus for supplying a large quantity of oil to friction members of a friction engagement element.
2. Description of the Related Art
An example of a brake employed in an automatic transmission to stop a rotatable element of a transmission mechanism is a friction engagement element of the wet multiple disc type. The conventional friction engagement element employed as a brake of an automatic transmission is controlled so that the engagement is completed in a short time and is exclusively used for speed shifts since the automatic transmission has a vehicle starting device such as a torque converter or the like. Therefore, although a transitional slipping state may occur during an engagement operation, no control operation is performed to intentionally keep friction members in a slipping state. The friction members of the friction engagement element are lubricated and cooled by lubricating oil released outward, by centrifugal force, from a supply opening of a lubricant passage formed in a rotating shaft located radially inward of the friction members. The lubricating oil splashed onto the friction members passes between the friction members thus lubricating various portions of the mechanism.
If a friction engagement element as described above is used as an engagement element in starting in motion a vehicle having a hybrid drive or a CVT (continuously variable transmission), i.e., a vehicle that is not equipped with a starting device such as a torque converter or the like, the friction engagement element must be slip-controlled for a considerably long period of time, unlike a friction engagement element employed for the purpose of a speed shift. In such slip control, a large quantity of heat is generated by the friction members, so that a large amount of lubricating oil must be supplied for cooling. Therefore, it becomes necessary to provide a lubricant passage (that allows a flow of about 7000 cc/min) separate from a conventional lubricant passage (that normally allows a flow of several hundred cc/min) provided for lubricating various portions of the mechanism.
An example of the above-described vehicle-starting clutch is disclosed in Japanese Patent Application Laid-Open No. HEI 9-60660. The disclosed structure includes a clutch cooling oil passage formed in a rotating shaft and a hub of a clutch drum fixed to the rotating shaft so that oil is supplied, by centrifugal force, from a supply opening formed in the drum-side of the hub that opens radially inward in the direction of the clutch hub and toward a friction member disposed between the clutch drum and the clutch hub. Escape of oil from a gap between the friction member and the clutch hub in a direction parallel to the axis of the clutch hub is prevented by a seal ring disposed between the clutch hub and a flange on an end portion of the friction member, so that substantially the entire amount of oil supplied to the friction member flows through the friction element.
A seal ring provides substantially complete prevention of oil supplied to the friction element from leaking in the axial direction, and thereby effectively reduces the loss of the supplied oil. However, in general, prevention of leakage by employment of a seal ring disposed between members that rotate relative to each other increases the friction loss due to the contact with the seal ring. Therefore, the above-described conventional structure is effective in a transmission wherein the increased sliding resistance does not pose a serious problem and, in particular, in a clutch wherein friction loss due to the sliding contact occurs only for a short period of time and wherein, during ordinary operation, there is no relative rotation between the friction member and the clutch hub. However, the above-described conventional structure is disadvantageous if incorporated into a hybrid drive train wherein increased sliding resistance should be avoided and, in particular, a brake wherein there is relative rotation between the friction member and the hub during normal operation.
Accordingly, it is an object of the invention to provide a friction engagement element (clutch or brake) lubricating system that is able to sufficiently cool and lubricate the friction members of the friction engagement element while reducing the loss of lubricant, without increase in sliding resistance even in controlled slippage.
In order to achieve the aforementioned and other objects, the present invention provides an apparatus including a friction engagement element and lubricating system therefor. The friction engagement element is arranged for engaging a rotating member with a case, and includes a hub connected to the rotating member, and at least one friction member disposed between the hub and the case, and an oil passage for supplying a lubricant from the case to the friction member. At least one discharge opening of the oil passage is provided radially inward of and to a first axial side of the friction element, which discharge opening is directed toward the friction member(s). A weir member is provided at a second axial side of the friction element to restrict escape of the lubricant axially through a gap between the hub and the friction member(s).
Therefore, the friction engagement element lubrication of the invention has a simple construction, yet is able to adequately lubricate the friction element. Furthermore, the apparatus prevents oil supplied from the first side in the axial direction from escaping toward the second side, and is able to hold oil at the radially inward side of the friction element.
In the above-described apparatus, the hub and the friction member may be connected by a spline arrangement in which keys (splines) are omitted at spline sites equidistantly and circumferentially spaced.
Therefore, the oil supplied to the radially inward side of the friction element can be uniformly distributed both axially and circumferentially to the entire space occupied by the friction element via the key-omitted sites. Hence, the entire friction element can be uniformly lubricated and cooled. Furthermore, the construction in which the key-omitted sites on the hub are utilized for delivery of lubricant in the axial direction is advantageous in eliminating the need for position alignment during the assembly step of mounting a plurality of friction members on the hub, and therefore provides easier assembly as compared with assembly of a prior art structure in which delivery of lubricant in the axial direction is accomplished by omitting keys on the friction members of the friction element or by forming an oil passage in the friction members.
The weir member may extend to a location that is radially inward of the outer periphery of the keys (splines) on the hub, to prevent the oil delivered through the sites where keys are omitted from the hub-side spline arrangement from escaping through a gap between the hub and the friction element.
The friction engagement element lubricating apparatus may further include a reaction member that is provided at a first axial side of the friction element and is supported by the case to bear the force exerted on the friction element by actuation of the hydraulic servo, wherein the oil passage is connected to a lubricant supply passage provided in the case, and wherein the oil passage and the oil discharge opening of the oil passage are formed in the reaction member. Hence, it becomes unnecessary to extend the case radially inward for the purpose of introducing lubricant. Furthermore, due to location of the oil passage in the reaction member, the number of component parts forming the lubricant passage is reduced.
The apparatus may further include return springs located radially outward of the friction member and extending between the weir member and the reaction member. Therefore, the weir member and the reaction member serve as return spring supports that are indispensable in the friction engagement element. Hence, it becomes possible to further reduce in number the component parts of the lubricating apparatus.
The oil passage may be a groove formed in the reaction member and closed by a lid member attached to the reaction member, and this oil passage may be connected with the lubricant supply passage formed in the case by an oil passage defined by a circumferential groove formed in the reaction member and the lid member. In this manner, the oil passage can be formed by an inexpensive processing method such as die-casting or the like. Still further, in comparison with a construction in which an oil passage is formed in a single member, the axial dimension, i.e, thickness, of the member forming the oil passage is reduced, allowing the overall axis dimension of the entire apparatus to be reduced.
The above-described apparatus may use plural discharge openings, optionally arranged around the circumference of a circle and optionally facing each other. Therefore, circumferential-direction unevenness in the supply of lubricant to the radially inward side of the friction member can be reduced. Hence, the supply of lubricant to the friction member can be made uniform in the circumferential direction as well, and unevenness in lubrication and cooling can be reduced.
Further, in the above-described apparatus, the friction member may have a cutout in the radially outward portion of the friction member. Therefore, the oil that has cooled the friction member and has reached the radially outward portion of the friction member can be moved in the axial direction to improve the oil discharge.
Alternatively, in the above-described apparatus, the reaction member may have a cutout in a surface of the reaction member that faces the case. Therefore, the discharge of the oil after cooling the friction member and reaching of the radially outward portion of the friction member can be improved.
The apparatus of the present invention may further include an engine, a planetary gear unit having at least three elements, and a transmission, wherein the output shaft of the engine is connected to one of the elements of the planetary gear unit, wherein an input shaft of the transmission is connected to another one of the elements of the planetary gear unit, and wherein the friction member is a brake for engaging still another one of the elements of the planetary gear unit with the case.
Therefore, through the slip control of the brake friction member, the rotation input to the transmission can be gradually increased in a direction of rotation opposite that of the engine.